The present invention relates to a new electronic weft or filling thread monitoring device on a gripper shuttle weaving machine or loom provided with means for returning, after thread insertion, the gripper shuttle from a stop position to a defined thread releasing position, and simultaneously tensioning the thread.
This new thread monitoring device comprises a device for sensing the weft or filling thread at the picking side of the weaving machine, a timing pulse generator actuated by the weaving machine, and a gating circuit operatively connected to the sensing device and the timing pulse generator, the gating circuit being locked for the output of the timing pulse generator as long as the sensing device produces a sensing signal indicative of proper thread insertion.
An electronic weft or filling thread monitor of the aforementioned type is disclosed by Swiss Pat. No. 437,163. This monitor comprises a thread sensing device arranged on the picking side of the weaving machine, following a thread tensioner, however outside the range thereof, and in advance of the selvedge of the textile web. The thread sensor is provided with a sensing pin or lever which is deflected or bent, during the tensioning or returning motion of the thread, by the transverse component of the tension exerted by the laterally deflected thread. The deflection of the thread is transformed into an electrical sensing signal indicative of an intact thread.
German patent publication No. 1,535,615 refers to another weft or filling thread monitor comprising, as a sensing element, a pivotable lever or rotatable roller arranged on the picking side antecedent to the thread tensioner, any motion of the sensing element being detected by optical means. This monitor responds to the so-called pull after motion occurring when the thread tensioner draws a short thread end off a supply spool and through the tensioner during the tensioning motion. Thus, a possible tensioning of the thread without longitudinal motion thereof does not result in a signal.
It is to be stated that the aforementioned thread monitors having a mechanical sensing element actuated by the weft or filling thread are affected by some inertia.
Moreover it is known to monitor the thread during insertion thereof into the waving shed. An electronic monitor designed for this purpose and comprising a sensing element arranged on the picking side is shown in Swiss Pat. No. 489,642 or U.S. Pat. No. 3,676,769. When the thread breaks during weft insertion, the monitor causes stopping the weaving machine. Electronic monitors of this type or thread insertion monitors by now are in widespread use. They are simple in construction and reliable in rugged long time operation. They also have sensing devices, such as triboelectrical sensors, which are substantially inertialess. Such sensors, by way of example, are disclosed in both last mentioned patents.
Due to the complicated operation of the gripper shuttle weaving machines, as compared with conventional weaving looms, the aforementioned known weft or filling thread monitors were not able to meet all desirable demands. In order to illustrate this situation, the intervals or phases of weft or filling thread insertion will be defined, and the occurring difficulties will be discussed in the following. As for the construction and operation of gripper shuttle weaving machines, both first mentioned patents are relevant.
The weft or filling thread insertion, prior and up to the controlled release of the thread from the gripper shuttle or projectile may be divided into three phases:
First phase: from picking the shuttle up to entering the receiving or catch box. The time interval of this phase, in the present context called insertion or weft insertion, depends upon the weaving width and may be, by way of example, 120 ms;
Second phase: time of shuttle braking and standstill in catch box. This "catch phase" is very short, and comprises, e.g., 10 ms;
Third phase: tensioning operation of thread tensioner and pulling back shuttle from stop position to thread release position in catch box. This "tensioning phase" may comprise 70 ms.
From experience, most of the thread breaks occur in the first and third phases, due to increased thread tension.
Particularly in the second phase, with the catch brake acting upon the projectile, the end of the inserted thread may prematurely be released from the projectile. Namely, due to strong deceleration forces, the pressure exerted by the thread clamping spring in the projectile may decrease to such a degree that the thread end is dropped (so-called looser). Moreover, when the thread brake is loosely adjusted, or loosened during operation, the projectile may hit the rear abutment of the breaking device in the catch box, also tending to release the thread end from the projectile (so-called rebounds).
All these various events are termed "thread breaks" in the following description. Since the aforesaid events result in fabric faults, they should be detected by a weft or filling thread monitor as completely as possible. That means, reliable thread monitoring should comprise thread insertion up to the end of the third phase, i.e. the tensioning phase. The very problem results from the difficulty to monitor the tensioning phase in such a manner that thread breaks are signalled safely and in time. This problem, due to the particular mode of operation of the gripper shuttle weaving machine, hitherto has not been solved satisfactorily.
When the projectile is being braked in the second phase, the thread slightly overshoots, because of the inertia thereof, tending to form so-called coilings in the thread end near the catch box. Since the thread brake arranged on the picking side is controllable, the undesired overshooting may be reduced, by increasing the braking effect, in such a manner that in the third phase this thread end is just sufficiently tensioned in the weaving shed. Then, during the tensioning motion there normally exists such a low thread tension that, when the thread is sensed between thread tensioner and weaving shed by known means, insufficient sensing signals are produced. This is also true in the above mentioned known case that the pull after motion is sensed between thread brake and thread tensioner, since only little or no thread is drawn from the supply coil through the thread brake.
These difficulties exist not only when using the above mentioned known weft or filling thread monitors provided with mechanical sensing elements, but also with electronic thread monitors having inertialess sensing elements mainly responsive to thread travel. This disadvantage might be partly avoided by increasing the effect of the thread brake; this, however causes further yarn breaks because of the increased thread tension, and thus reduces the efficiency of the machine.